Peptide and Protein Mimetics Inhibiting Amyloid beta-Peptide Aggregation

Protein misfolding is related to some fatal diseases including Alzheimer's disease (AD). Amyloid beta-peptide (A beta) generated from amyloid precursor protein can aggregate into amyloid fibrils, which are known to be a major component of A beta deposits (senile plaques). The fibril formation of A beta is typical of a nucleation-dependent process through self-recognition. Moreover, during fibrillization, several metastable intermediates such as soluble oligomers, including A beta-derived diffusible ligands (ADDLs) and A beta*56, are produced, which are thought to be the most toxic species to neuronal cells. Therefore, construction of molecules that decrease the A beta aggregates, including soluble oligomers, protofibrils, and amyloid fibrils, might further our understanding of the mechanism(s) behind fibril formation and enable targeted drug discovery against AD. To this aim, various peptides and peptide derivatives have been constructed using the A beta binding element based on the structural models of A beta amyloid fibrils and the mechanisms of self-assembly. The central hydrophobic amino acid sequence, LVFF, of A beta is a key sequence to self-assemble into amyloid fibrils. By combination of this core sequence with a hydrophobic or hydrophilic moiety, such as cholic acid or aminoethoxy ethoxy acetic acid units, respectively, good inhibitors of A beta aggregation can be designed and synthesized. A peptide, LF, consisting of the sequence Ac-KQKLLLFLEE-NH(2), was designed based on the core sequence of A beta but with a simplified amino acid sequence. The LF peptide can form amyloid-like fibrils that efficiently coassemble with mature A beta 1-42 fibrils. The LF peptide was also observed to immediately transform the soluble oligomers of A beta 1-42, which are thought to pose toxicity in AD, into amyloid-like fibrils. On the other hand, two A beta-like beta-strands with a parallel orientation were embedded in green fluorescent protein (GFP), comprised of a beta-barrel structure, to make pseudo-A beta beta-sheets on its surface. The GFP variant P13H binds to A beta 1-42 and inhibits A beta 1-42 oligomerization effectively in a substoichiometric condition. Thus, molecules capable of binding to A beta can be designed based on structural similarities with the A beta molecule. The peptide and protein mimetics based on the structural features of A beta might lead to the development of drug candidates against AD.